Rebels, exiled political opposition, West and Gulf Arabs say no credible vote can be held in country where swathes of territory are outside state control.

Syrians voted on Tuesday in an election expected to deliver an overwhelming victory for President Bashar Assad in the midst of a devastating civil war but which his opponents have dismissed as a charade.

Rebel fighters, the political opposition in exile, Western powers and Gulf Arabs say no credible vote can be held in a country where swathes of territory are outside state control and millions of people have been displaced in the conflict, which grew from protests against Assad's rule.

Insurgents battling to overthrow Assad stepped up attacks in government-controlled areas in the buildup to the election, seeking to disrupt the vote.

Polling stations opened at 7 a.m. (0400 GMT) in parts of Syria where Assad continues to rule. State television showed thousands of people queuing to vote, as well as crowds waving Syrian flags and portraits of the 48-year-old leader.

"We hope for security and stability," said Hussam al-Din al Aws, an Arabic teacher who was the first person to vote at a polling station at a Damascus secondary school. Asked who would win, he responded: "God willing, President Bashar Assad."

Assad is running against two relatively unknown challengers who were approved by a parliament packed with his supporters, the first time in half a century that Syrians have been offered any choice of candidates.

The last seven presidential votes were referenda to approve Bashar or his father, Hafez al-Assad. Hafez never scored less than 99 percent, while his son got 97.6 percent seven years ago.

Neither of Assad's rivals, former minister Hassan al-Nouri or parliamentarian Maher Hajjar, is expected to make major inroads into those levels of support.

"It's a tragic farce," French Foreign Minister Laurent Fabius said. "The Syrians in a zone controlled by the Syrian government have a choice of Bashar or Bashar. This man has been described by the UN Secretary General as a criminal," he told France 2 television.

Syrian officials confidently predicted a big turnout and said that a high level of participation would be as significant as the result itself.

"The size of the turnout is a political message," Information Minister Omran Zoabi told Reuters on Monday night. "The armed terrorist groups have increased their threats because they fear (a high level of) participation," he said, referring to the rebels.

"If these terrorist groups had any popularity it would be enough to ensure the failure of the election," he said.

"But they realize they have no popularity, so they want to affect the level of participation so they can say the turnout was low."

Tens of thousands of Syrian expatriates and refugees cast their ballots last week in an early round of voting, although the number was just a fraction of the nearly 3 million refugees and other Syrians living abroad.

The election took place three years after protests first broke out in Syria, calling for democratic reform in a country dominated since 1970 by the Assad family. Authorities responded with force and the uprising descended into civil war.

Assad's forces, backed by allies including Iran and Lebanon's militant group Hezbollah, have consolidated their control in central Syria but the insurgents and foreign jihadi fighters hold broad expanses of northern and eastern Syria.

Peace talks in Geneva between the government and the opposition National Coalition, which the opposition said must be based on the principle of Assad stepping aside in favor of a transitional government, collapsed in February.

Since then Assad's forces and Hezbollah fighters have seized back control of former rebel strongholds on the Lebanese border, cutting off supply lines for weapons and fighters, and the last rebels have retreated from the center of the city of Homs.

The withdrawal from Homs has focused attention on the northern city of Aleppo, formerly Syria's commercial hub, where fighting has escalated in the last few weeks.

Rebel rocket fire on government-controlled areas of Aleppo killed 50 people over the weekend, while barrel bombs dropped by army helicopters on rebel-held areas of Aleppo have killed nearly 2,000 people this year, a monitoring group said.

State media said on Monday that a car bomb killed at least 10 people in Homs province.